I visited the café on holiday a few years ago and the Gingerbread was stunning. I did email Jonathan for the recipe, he replied:
That is a top secret recipe, but to help guide you we use extra ginger (i.e. ginger powder and fresh ginger), Welsh Stout and Welshman’s Caviar (his dried Laver product name – apparently a phrase coined by the Welsh actor Richard Burton).
You can watch the episode here – forward to 21:12 (to 28:26).
My only criticism is I disagree with pulling seaweed directly off the rocks, I recommend cutting it.